Madonna and Sting have shown their support for jailed Russian punk band Pussy Riot.

The group are currently on trial in Moscow accused of hooliganism on the grounds of religious hatred after they performed a song mocking Russian President Vladimir Putin on the altar of an Orthodox cathedral.

Amnesty International has condemned the Russian authorities' treatment of Maria Alekhina, Ekaterina Samutsevich and Nadezhda Tolokonnikova, who face up to seven years in prison.

In a statement on his website, Sting said: "It's appalling that the musicians from Pussy Riot could face prison sentences of up to seven years in jail. Dissent is a legitimate and essential right in any democracy and modern politicians must accept this fact with tolerance.

"A sense of proportion - and a sense of humor - is a sign of strength, not a sign of weakness. Surely the Russian authorities will completely drop these spurious charges and allow the women, these artists, to get back to their lives and to their children."

Red Hot Chili Peppers' Anthony Kiedis and Flea have written letters of support to Tolokonnikova's husband Pyotr Verzilov, with Kiedis wearing a Pussy Riot T-shirt during a performance in Moscow on Sunday, according to Rolling Stone.

Madonna told a Russian TV channel that she was "sorry" to hear of the band's arrest, while Peter Gabriel and Franz Ferdinand singer Alex Kapranos have also expressed their support.

Amnesty has declared the women "prisoners of conscience", with many viewing the arrests as a government-led crackdown on freedom of expression.